This question can be answered with the basic laws of motion. Since the question is asking for FORCE, we know we must need this equation:
[tex]F = m*a[/tex]
Since we know m but don't know a, we must find it using another equation. The one to use is:
[tex]a = (v_{f} - v_{i}) * t[/tex]
where [tex](v_{f} - v_{i})[/tex] = the change in velocity. In this case the change comes out negative since the car is slowing down, and, you will notice that your answer will be a negative number to reflect this. Leave the negative symbol in your answer.
Now that you have a, simply solve for F above using F = m x a.
